An apparatus of the kind described is typified by an arrangement in which a light receptor or collector having the end face of an optical fibre disposed at the focal position of an optical lens thereof is driven in a tracking manner. One such arrangement comprises a vertical stanchion disposed in an upright position with respect to a horizontal plane and rotatable about a vertical axis through an angular range substantially equal to 180.degree. from the east to the west orientation, a light receptor support frame carried in a horizontal plane by the stanchion so as to be rotatable about a horizontal axis, an azimuth drive mechanism for rotatively driving the stanchion about the vertical axis, and an elevation drive mechanism carried by the azimuth drive mechanism for driving the receptor support frame for rotation about the horizontal axis, as disclosed in Japanese Patent Publication No. 73,922/1992. A support arrangement of the described type requires a rigid structure to support the vertical stanchion against an increased load which results when it is desired to increase a light receiving area. Specifically, as the light receiving area is increased, the receptor gains its height, necessitating a design which assures a more firm support for the stability of the receptor together with a more rigid structure to withstand a resulting increased wind pressure. Also there arises a concern that the structure may interrupt the incidence of sunbeam to a third party land located around or adjacent to the lot where the solar radiation utilization mechanism is installed. On the other hand, if the light receiving area per unit or individual receptor is decreased while a number of receptor supports are arranged in a matrix array, the wind pressure load on each unit can be minimized and no undue strength is required for the receptor support structure. This also avoids the possibility of intercepting the incidence of sunbeam onto a third party land. However, because each unit must be provided with an azimuth and an elevation drive mechanism, the number of such drive mechanisms required for the total light receiving area or the bank of receptor supports in the matrix array will be prohibitive, resulting in an inefficiency in the mechanism investment.
Japanese Patent Publication No. 47,801/1992 discloses a three-axis receptor support arrangement including a support framework which is mounted on the vertical stanchion that is rotatively driven by the azimuth drive mechanism and which is driven for rotation about an east-west axis, the support framework carrying a number of elevation drive mechanisms, each of which is operable to support the base of an individual receptor. Since a plurality of elevation mechanisms are supported by a single azimuth mechanism, this reduces the total number of drive mechanisms for the total light receiving area, providing an advantage in respect of mechanism investment. However, the single vertical stanchion must support the framework carrying the entire elevation mechanisms for rotation in the azimuth direction, and accordingly, the load on the stanchion increases and therefore there must be provided a strengthened support structure.
A most typical light collector of the prior art is designed such that a front end face of an optical fibre is positioned at the focus of a condenser lens, an example being disclosed in Japanese Patent Publication No. 44,282/1991. A convex lens is not suitable for use as a solar radiation condenser lens since an increased thickness results for a larger diameter collector. Fresnel lens is in the form of a plate of a reduced thickness, which does not increase significantly even for a larger diameter collector, and thus is adequate to be used as a condenser lens. However, when the angle of incidence of light upon the front end face of the optical fibre or the angle with respect to the centerline of the optical fibre increases, the light will be reflected by the total reflection and cannot pass into the optical fibre. Thus if a Fresnel lens is used which has a large diameter of its light responsive area combined with a reduced focal length, the majority of condensed light cannot find its way into the optical fibre and there occurs a need to increase the focal length as the collector area or its diameter is increased. This results in increasing the distance between the lens and the front end face of the optical fibre, and thus results in a light collector which exhibits an increased thickness or tallness in a direction toward the sun. To avoid this, the common practice has been to provide a honeycomb array comprising a number of lenses of a reduced diameter in order to construct an extensive light receiving surface, with the front end face of each optical fibre positioned at the focal position of each individual lens, as disclosed in Japanese Patent Publication No. 44,282/1991. Also a solar radiation collector system is disclosed in Japanese Patent Publication No. 73,922/1992 which controls a light collector comprising a honeycomb array of small diameter lenses so as to be oriented toward the sun.
It is to be noted however that the light receiving area per fibre is reduced, and consequently, the number of fibres must be increased in order to provide an extensive light receiving area. When the light receiving area per fibre is small, the amount of light which must be transmitted is low, and hence an optical fibre of a reduced diameter can be used. On the other hand, an increasing difficulty is experienced, as the fibre diameter is reduced, in properly positioning and maintaining the front end face of the fibre in focus as the motion of the sun is being tracked. Because of such difficulty, the diameter of the optical fibre cannot be reduced significantly, resulting in using an excessive amount of optical fibre material.
A heat collector, that is, a light receptor which receives solar radiation and converts it into heat is known in the art in which a piping with a black surface is disposed for purpose of photo-thermal conversion process at the focal position of a convex lens or a mirror which is semicircular or parabolic in cross section and which is elongate longitudinally with a flow of water being passed through the piping to serve as a conversion process fluid. For the reason as mentioned previously, a convex lens is not preferred as a condenser lens, but Fresnel lens is preferred. Since the light will be reflected by the total reflection to degrade the light collection efficiency if an angle of incidence of the light upon the photo-thermal conversion surface or the angle with respect to a perpendicular to the surface is large, it is necessary to increase the focal length as the diameter (or area) of the light receiving surface of the lens is increased. This remains true if a mirror is used. The consequence of this shows up as a heat collector which is tall in a direction toward the sun. Light condensing or focussing effect takes place in the transverse section, but does not take place in the longitudinal direction, resulting in a low light collection density and rendering it difficult to achieve a heat collection to an elevated temperature.